The present application relates to nuclear magnetic resonance (NMR) spectroscopy and, more particularly, to novel NMR spectroscopy body probes having at least one surface coil.
It is known to utilize surface coil NMR spectroscopy for studying living tissue by imaging spectra from atoms, such as .sup.1 H, .sup.13 C, .sup.19 F, .sup.31 P, and the like, having an odd number of nucleons. Studies of cerebral ischaemia, stroke and myocardial infarct drug therapy efficacy have all been carried out utilizing NMR spectroscopy. In the typical NMR spectroscopy experiment, the living tissue is immersed in a substantially homogeneous static magnetic field B.sub.0, typically directed along one axis, e.g. the Z axis, of a threedimensional Cartesian set of coordinates. Under the influence of the magnetic field B.sub.0, the nuclei (and therefore the net magnetization M) precess or rotate about the axis of the field. The rate, or frequency, at which the nuclei precess is dependent upon the strength of the applied magnetic field and on the nuclei characteristics. The angular frequency of precession .omega., is defined as the Larmor frequency and is given by the equation: .omega.=.gamma.B.sub.0, in which .gamma. is the gyromagnetic ratio (constant for each type of nucleus). The frequency at which the nuclei precess is therefore substantially dependent on the strength of the magnetic field B.sub.0, and increases with increasing field strength. Because the precessing nucleus is capable of absorbing and re-radiating electromagnetic energy, a radio-frequency (RF) magnetic field at the Larmor frequency can be utilized to excite the nuclei and receive imaging response signals therefrom. It is possible, by superimposing one or more magnetic field gradients of sufficient strength, to spread out the NMR signal spectrum of the sample and thereby distinguish NMR signals arising from different spatial postions in the sample, based on their respective resonant frequencies. Spatial positions of the NMR signals are determinable by Fourier analysis and knowledge of the configuration of the applied magnetic field gradient, while chemical-shift information can be obtained to provide spectroscopic images of the distribution of a particular specie of nucleus within the imaged sample.
Because the various nuclei to be investigated by NMR spectroscopy have widely differing values of the gyromagnetic constant .gamma., the resonant frequencies of these nuclei will vary over a similarly large range. Therefore, a surface coil properly tuned to one of the nuclei resonances will be improperly tuned at other nuclei resonant frequencies. Further, as a surface coil probe must be positioned in close proximity to the exterior of the sample portion to be image, the surface coil probe so positioned will allow the RF electric field of the probe to undesirably heat the imaged sample. The RF electric field is unnecessary, as only the RF magnetic field is needed for NMR imaging and spectroscopy.
Accordingly, it is desirable to provide NMR spectroscopy body probes with at least one surface coil, having a reduced electric field, capable of being conformally fitted to the exterior surface of the sample to be investigated, and capable of exciting a selected one, or a plurality, of several nuclei resonances without the necessity for surface probe changing, retuning or any other time-consuming adjustments.